Low power consumption memory device

ABSTRACT

A memory device includes a memory cell, a local bit line, a data line, first and second pass gate circuits, and a sense amplifier. The local bit line is coupled to the memory cell. The first pass gate circuit is coupled to the local bit line and the data line and is configured to couple the local bit line to the data line. The second pass gate circuit is coupled to the data line and the global bit line and is configured to couple the data line to the global bit line. The sense amplifier is coupled to the data line.

BACKGROUND

A conventional memory device includes a memory cell, a local bit line, aglobal bit line, a word line, a pass gate circuit, a pre-charger, and across-coupled p-channel metal-oxide semiconductor field-effecttransistors (MOSFETs) circuit. Prior to a write operation of the memorydevice, the pre-charger pre-charges the local bit line to a high voltagelevel, e.g., a level of a source voltage at which the memory device isoperated. Thereafter, the local bit line is left floating at the highvoltage level.

During a write operation of the memory device, a low voltage level,e.g., a level of a ground voltage of the memory device, is firstprovided to the global bit line. Then, the pass gate circuitelectrically couples the local bit line to the global bit line. Thistransfers the low voltage level from the global bit line to the localbit line. This, in turn, pulls the local bit line from the high voltagelevel towards the low voltage level. Subsequently, the cross-coupledp-channel MOSFETs circuit pulls the local bit line to the low voltagelevel. At this time, the word line is activated, whereby a bit ‘0’ ofdata is written to the memory cell. Such a write operation consumes alarge amount of power.

BRIEF DESCRIPTION OF THE DRAWINGS

Aspects of the present disclosure are best understood from the followingdetailed description when read with the accompanying figures. It isnoted that, in accordance with the standard practice in the industry,various features are not drawn to scale. In fact, the dimensions of thevarious features may be arbitrarily increased or reduced for clarity ofdiscussion.

FIG. 1 is a flow chart of an exemplary method of performing read andwrite operations in a memory device according to some embodiments.

FIG. 2 is a schematic diagram of an exemplary memory device according tosome embodiments.

FIG. 3 is a schematic diagram of an exemplary memory cell of the memorydevice according to some embodiments.

FIGS. 4A and 4B are schematic diagrams of the memory cell during aread/write operation of the memory device according to some embodiments.

FIG. 5 is a schematic diagram of an exemplary read/write circuit unit ofthe memory device according to some embodiments.

FIGS. 6A and 6B are schematic diagrams of the read circuit unit during aread operation of the memory device according to some embodiments.

FIGS. 7A and 7B are schematic diagrams of the write circuit unit duringa write operation of the memory device according to some embodiments.

FIGS. 8 and 9 are schematic diagrams of exemplary voltage generatingcircuits of the memory device according to some embodiments.

DETAILED DESCRIPTION

The following disclosure provides many different embodiments, orexamples, for implementing different features of the provided subjectmatter. Specific examples of components and arrangements are describedbelow to simplify the present disclosure. These are, of course, merelyexamples and are not intended to be limiting. For example, the formationof a first feature over or on a second feature in the description thatfollows may include embodiments in which the first and second featuresare formed in direct contact, and may also include embodiments in whichadditional features may be formed between the first and second features,such that the first and second features may not be in direct contact. Inaddition, the present disclosure may repeat reference numerals and/orletters in the various examples. This repetition is for the purpose ofsimplicity and clarity and does not in itself dictate a relationshipbetween the various embodiments and/or configurations discussed.

Further, spatially relative terms, such as “beneath,” “below,” “lower,”“above,” “upper” and the like, may be used herein for ease ofdescription to describe one element or feature's relationship to anotherelement(s) or feature(s) as illustrated in the figures. The spatiallyrelative terms are intended to encompass different orientations of thedevice in use or operation in addition to the orientation depicted inthe figures. The apparatus may be otherwise oriented (rotated 90 degreesor at other orientations) and the spatially relative descriptors usedherein may likewise be interpreted accordingly.

The present disclosure provides a memory device that includes a readcircuit unit and a write circuit unit. The read circuit unit includes asense amplifier that senses a difference between levels of voltages oncomplementary data lines of the memory device and that amplifies thedifference sensed thereby. As will be described in detail herein, thewrite circuit unit exploits the sense amplifier of the read circuit unitso as to conserve power consumption of the memory device.

A flow chart of an exemplary method of performing read and writeoperations in a memory device, according to some embodiments, isillustrated in FIG. 1. The memory device includes complementary datalines, e.g., complementary data lines (DL, DLB) of FIG. 5, complementaryfirst global bit lines, e.g., complementary global bit lines (RGBL,RGBLB) of FIG. 5, complementary second global bit lines, e.g.,complementary global bit lines (WGBL, WGBLB) of FIG. 5, complementarylocal bit lines, e.g., complementary local bit lines (BL, BLB) of FIG.5, a memory cell, a pre-charger, a read circuit unit, and a writecircuit unit. Prior to operation 110, the data lines are pre-charged bythe pre-charger to a high voltage level, e.g., a level of a sourcevoltage at which the memory device is operated. In operation 110, a readis performed on the memory cell using a sense amplifier of the readcircuit unit. In some embodiments, operation 110 includes the senseamplifier sensing a difference between levels of voltages on the datalines and amplifying the difference sensed thereby, i.e., pulling one ofthe data lines to a low voltage level, e.g., a level of a referencevoltage of the memory device. In some embodiments, operation 110includes transferring the low and high voltage levels from the datalines to the first global bit lines, respectively, whereby complementarybits of data are read from the memory cell.

Prior to operation 120, the data lines are pre-charged by thepre-charger to the high voltage level. In operation 120, a write isperformed on the memory cell using the sense amplifier of the readcircuit unit. In some embodiments, operation 120 includes transferring alow power consumption voltage from one of the second global bit lines toone of the data lines. The low power consumption voltage has a levellower than the high voltage level but higher than the low voltage leveland in some embodiments is generated by a voltage generating circuit ofthe write circuit unit. In some embodiments, operation 120 includes thesense amplifier sensing a difference between levels of voltages on thedata lines and amplifying the difference sensed thereby, i.e., pullingone of the data lines to the low voltage level. In some embodiments,operation 120 includes transferring the high and low voltage levels fromthe data lines to the local bit lines, respectively, wherebycomplementary bits of data are written to the memory cell.

A schematic diagram of an exemplary memory device 200, according to someembodiments, is illustrated in FIG. 2. The memory device 200 includescomplementary data lines (DL, DLB), complementary global bit lines(RGBL, RGBLB), complementary global bit lines (WGBL, WGBLB),complementary local bit lines (BL, BLB), a memory cell 210, a readcircuit unit, and a write circuit unit. In this exemplary embodiment,the memory device 200 is implemented using metal-oxide semiconductorfield-effect transistors (MOSFETs). It should be understood that aMOSFET has first and second source/drain terminals and a gate terminal.In an alternative embodiment, the memory device 200 may be implementedwith any type of transistor. In some embodiments, the memory device 200is a static random access memory (SRAM) device. In other embodiments,the memory device 200 is a dynamic RAM (DRAM) device.

The memory cell 210 is connected to the local bit lines (BL, BLB) and isconfigured to store complementary bits of data therein. A schematicdiagram of an exemplary memory cell 210 of the memory device 200,according to some embodiments, is illustrated in FIG. 3. In thisexemplary embodiment, the memory cell 210 is a six-transistor (6T)memory cell and includes a source voltage node 310, a reference voltagenode 320, memory cell nodes 330, 340, p-channel MOSFETs (M1, M2), andn-channel MOSFETs (M3, M4, M5, M6). The memory cell 210 is configured tostore a bit ‘0’ or a low voltage level, i.e., a level of a referencevoltage (VSS), e.g., 0 V, applied at the reference voltage node 320, anda bit ‘1’ or a high voltage level, i.e., a level of a source voltage(VDD), e.g., 1 V, applied at the source voltage node 310. In someembodiments, the memory cell 210 may include any number of MOSFETs. Inother embodiments, the memory cell 210 may have other configurations solong as it can store complementary bits of data therein.

The p-channel MOSFETs (M1, M2) and the n-channel MOSFETs (M3, M4)constitute a latch. The first source/drain terminals of the p-channelMOSFETs (M1, M2) are connected to each other and to the source voltagenode 310. The first source/drain terminals of the n-channel MOSFETs (M3,M4) are connected to each other and to the reference voltage node 320.The second source/drain terminals of the p-channel and n-channel MOSFETs(M1, M3) and the gate terminals of the p-channel and n-channel MOSFETs(M2, M4) are connected to each other and to the memory cell node 330.The second source/drain terminals of the p-channel and n-channel MOSFETs(M2, M4) and the gate terminals of the p-channel and n-channel MOSFETs(M1, M3) are connected to each other and to the memory cell node 340.

The first source/drain terminals of the n-channel MOSFETs (M5, M6) arerespectively connected to the local bit lines (BL, BLB). The secondsource/drain terminals of the n-channel MOSFETs (M5, M6) arerespectively connected to the memory cell nodes 330, 340. The memorydevice 200 further includes a word line (WL). The gate terminals of then-channel MOSFETs (M5, M6) are connected to each other and to the wordline (WL).

Schematic diagrams of the memory cell 210 during a read/write operationof the memory device 200, according to some embodiments, are illustratedin FIGS. 4A and 4B. As illustrated in FIG. 4A, during a read operation,in which bits ‘1’ and ‘0’ are respectively latched/stored in the memorycell nodes 330, 340, the p-channel and n-channel MOSFETs (M1, M4) areturned on. The p-channel and n-channel MOSFETs (M2, M3) are turned offand are therefore crossed out in FIG. 4A. At this time, when a voltageon the word line (WL) transitions from the low voltage level to the highvoltage level, i.e., when the word line (WL) is activated, the n-channelMOSFETs (M5, M6) are turned on and connect electrically and respectivelythe local bit lines (BL, BLB) to the memory cell nodes 330, 340. As aresult, the bits ‘1’ and ‘0’ are respectively transferred from thememory cell nodes 330, 340 to the local bit lines (BL, BLB), wherebycomplementary bits of data are read from the memory cell 210.

As illustrated in FIG. 4B, during another read operation of the memorydevice 200, in which bits ‘0’ and ‘1’ are respectively stored in thememory cell nodes 330, 340, the p-channel and n-channel MOSFETs (M2, M3)are turned on. The p-channel and n-channel MOSFETs (M1, M4) are turnedoff and are therefore crossed out in FIG. 4B. At this time, when theword line (WL) is activated, the n-channel MOSFETs (M5, M6) are turnedon and connect electrically and respectively the local bit lines (BL,BLB) to the memory cell nodes 330, 340. As a result, the bits ‘0’ and‘1’ are respectively transferred from the memory cell nodes 330,340 tothe local bit lines (BL, BLB), whereby complementary bits of data areread from the memory cell 210.

Referring back to FIG. 4A, during a write operation of the memory device200, in which bits ‘1’ and ‘0’ are respectively on the local bit lines(BL, BLB), when the word line (WL) is activated, the n-channel MOSFETs(M5, M6) are turned on and connect electrically and respectively thelocal bit lines (BL, BLB) to the memory cell nodes 330, 340. As aresult, the bits ‘1’ and ‘0’ are respectively transferred from the localbit lines (BL, BLB) to the memory cell nodes 330, 340. At this time, thep-channel and n-channel MOSFETs (M1, M4) are turned on and the p-channeland n-channel MOSFETs (M2, M3) are turned off, whereby complementarybits of data are written to the memory cell 210.

Referring now to FIG. 4B, during another write operation of the memorydevice 200, in which bits ‘0’ and ‘1’ are respectively on the local bitlines (BL, BLB), when the word line (WL) is activated, the n-channelMOSFETs (M5, M6) are turned on and connect electrically and respectivelythe local bit lines (BL, BLB) to the memory cell nodes 330, 340. As aresult, the bits ‘0’ and ‘1’ are respectively transferred from the localbit lines (BL, BLB) to the memory cell nodes 330,340. At this time, thep-channel and n-channel MOSFETs (M2, M3) are turned on and the p-channeland n-channel MOSFETs (M1, M4) are turned off, whereby complementarybits of data are written to the memory cell 210.

It should be understood that the memory device 200 may include aplurality of banks, each of which includes a plurality of the memorycells 210 that are arranged in rows and columns.

Referring back to FIG. 2, the memory device 200 further includes anoutput circuit 220 connected to the data lines (DL, DLB) and configuredto generate an output voltage, a level of which corresponds to a voltagelevel on the data line (DL/DLB).

The read circuit unit includes a pass gate circuit 230, a senseamplifier 240, and an enable circuit 250. The pass gate circuit 230 isconnected to the local bit lines (BL, BLB) and the data lines (DL, DLB)and is configured to electrically and respectively connect the local bitlines (BL, BLB) to the data lines (DL, DLB). The sense amplifier 240 isconnected to the data lines (DL, DLB) and is configured to sense adifference between levels of voltages on the data lines (DL, DLB) and toamplify the difference sensed thereby. The enable circuit 250 isconnected to the output circuit 220 and the global bit lines (RGBL,RGBLB) and is configured to provide the output voltage generated by theoutput circuit 220 to the global bit line (RGBL/RGBLB).

A schematic diagram of an exemplary read/write circuit unit of thememory device 200, according to some embodiments, is illustrated in FIG.5. The output circuit 220 includes n-channel MOSFETs (M1, M2) andinverters (INV1, INV2) respectively between the data line (DL) and thegate terminal of the n-channel MOSFET (M1) thereof and between the dataline (DLB) and the gate terminal of the n-channel MOSFET (M2) thereof

The pass gate circuit 230 includes an enable node (RPG) and p-channelMOSFETs (M1, M2). The first source/drain terminals of the p-channelMOSFETs (M1, M2) of the pass gate circuit 230 are respectively connectedto the local bit lines (BL, BLB). The second source/drain terminals ofthe p-channel MOSFETs (M1, M2) of the pass gate circuit 230 arerespectively connected to the data lines (DL, DLB). The gate terminalsof the p-channel MOSFETs (M1, M2) of the pass gate circuit 230 areconnected to each other and to the enable node (RPG).

The sense amplifier 240 includes an enable node (SAE), p-channel MOSFETs(M1, M2), and n-channel MOSFETs (M3, M4, M5). The first source/drainterminals of the p-channel MOSFETs (M1, M2) of the sense amplifier 240are connected to each other and to the source voltage node 310. Thefirst source/drain terminals of the n-channel MOSFETs (M3, M4, M5) ofthe sense amplifier 240 are connected to each other. The secondsource/drain terminal and the gate terminal of the n-channel MOSFET (M5)of the sense amplifier 240 are respectively connected to the referencevoltage node 320 and the enable node (SAE). The second source/drainterminals of the p-channel and n-channel MOSFETs (M1, M3) and the gateterminals of the p-channel and n-channel MOSFETs (M2, M4) of the senseamplifier 240 are connected to each other and to the data line (DL). Thesecond source/drain terminals of the p-channel and n-channel MOSFETs(M2, M4) and the gate terminals of the p-channel and n-channel MOSFETs(M1, M3) of the sense amplifier 240 are connected to each other and tothe data line (DLB).

The enable circuit 250 includes an enable node (RE) and n-channelMOSFETs (M1, M2). The first source/drain terminals of the n-channelMOSFETs (M1, M2) of the enable circuit 250 are respectively connected tothe first source/drain terminals of the n-channel MOSFETs (M1, M2) ofthe output circuit 220. The second source/drain terminals of then-channel MOSFETs (M1, M2) of the enable circuit 250 are respectivelyconnected to the global bit lines (RGBL, RGBLB). The gate terminals ofthe n-channel MOSFETs (M1, M2) of the enable circuit 250 are connectedto each other and to the enable node (RE). The gate terminals of then-channel MOSFETs (M1, M2) of the enable circuit 250 are connected toeach other and to the enable node (RE). The second source/drainterminals of the n-channel MOSFETs (M1, M2) of the output circuit 220are connected to each other and to the reference voltage node 320.

The memory device 200 further includes a pre-charger 510 connected tothe data lines (DL, DLB) and configured to pre-charge the data lines(DL, DLB) to the high voltage level. In this exemplary embodiment, thepre-charger 510 includes an enable node (SAPGB) and p-channel MOSFETs(M1, M2). The first source/drain terminals of the p-channel MOSFETs (M1,M2) of the pre-charger 510 are connected to each other and to the sourcevoltage node 310. The second source/drain terminals of the p-channelMOSFETs (M1, M2) of the pre-charger 510 are respectively connected tothe data lines (DL, DLB). The gate terminals of the p-channel MOSFETs(M1, M2) of the pre-charger 510 are connected to each other and to theenable node (SAPGB).

Schematic diagrams of the read circuit unit during a read operation ofthe memory device 200, according to some embodiments, are illustrated inFIGS. 6A and 6B. Prior to a read operation, when a voltage at the enablenode (SAPGB) transitions from the high voltage level to the low voltagelevel, the p-channel MOSFETs (M1, M2) of the pre-charger 510 are turnedon. As a result, the data lines (DL, DLB) are pre-charged to the highvoltage level. Subsequently, when the voltage at the enable node (SAPGB)transitions from the low voltage level back to the high voltage level,the p-channel MOSFETs (M1, M2) of the pre-charger 510 are turned off. Asa result, the data lines (DL, DLB) are left floating at the high voltagelevel.

As illustrated in FIG. 6A, during a read operation of the memory device200, in which bits ‘1’ and ‘0’ are respectively latched/stored in thememory cell nodes 330, 340 of the memory cell 210, when a voltage at theenable node (RPG) transitions from the high voltage level to the lowvoltage level, the p-channel MOSFETs (M1, M2) of the pass gate circuit230 are turned on and connect respectively and electrically the localbit lines (BL, BLB) to the data lines (DL, DLB). At this time, the wordline (WL) is activated. As a result, the bits ‘1’ and ‘0’ arerespectively transferred from the local bit lines (BL, BLB) to the datalines (DL, DLB). This pulls the data line (DLB) towards the low voltagelevel. As this occurs, the data line (DL) stays at the high voltagelevel. The p-channel and n-channel MOSFETs (M2, M3) of the senseamplifier 240 are turned off and are therefore crossed out in FIG. 6A.

When the sense amplifier 240 senses that a difference between the levelsof the voltages on the data lines (DL, DLB) is greater than a thresholdvoltage, e.g., 100 mV, a voltage at the enable node (SAE) transitionsfrom the low voltage level to the high voltage level. This pulls thedata line (DLB) to the low voltage level. At this time, a voltage at theenable node (RE) is at the high voltage level. As a result, the lowlevel voltage is transferred from the data line (DLB) to the global bitline (RGBLB) by the output circuit 220 through the n-channel MOSFET (M2)of the enable circuit 250, whereby complementary bits of data are readfrom the memory cell 210.

As illustrated in FIG. 6B, during another read operation of the memorydevice 200, in which bits ‘0’ and ‘1’ are respectively stored in thememory cell nodes 330, 340 of the memory cell 210, when a voltage at theenable node (RPG) transitions from the high voltage level to the lowvoltage level, the p-channel MOSFETs (M1, M2) of the pass gate circuit230 are turned on and connect respectively and electrically the localbit lines (BL, BLB) to the data lines (DL, DLB). At this time, the wordline (WL) is activated. As a result, the bits ‘0’ and ‘1’ arerespectively transferred from the local bit lines (BL, BLB) to the datalines (DL, DLB). This pulls the data line (DL) towards the low voltagelevel. As this occurs, the data line (DLB) stays at the high voltagelevel. The p-channel and n-channel MOSFETs (M1, M4) of the senseamplifier 240 are turned off and are therefore crossed out in FIG. 6B.

When the sense amplifier 240 senses that a difference between the levelsof the voltages on the data lines (DL, DLB) is greater than a thresholdvoltage, e.g., 100 mV, a voltage at the enable node (SAE) transitionsfrom the low voltage level to the high voltage level. This pulls thedata line (DL) to the low voltage level. At this time, a voltage at theenable node (RE) is at the high voltage level. As a result, the lowlevel voltage is transferred from the data line (DL) to the global bitline (RGBL) by the output circuit 220 through the n-channel MOSFET (M1)of the enable circuit 250, whereby complementary bits of data are readfrom the memory cell 210.

Referring back to FIG. 2, the write circuit unit includes a pass gatecircuit 260, a keeper 270, an enable circuit 280, and a voltagegenerating circuit 290. The pass gate circuit 260 is connected to thedata lines (DL, DLB) and the global bit lines (WGBL, WGBLB) and isconfigured to electrically and respectively connect the data lines (DL,DLB) to the global bit lines (WGBL, WGBLB). The keeper 270 is connectedto the local bit lines (BL, BLB) and is configured in this exemplaryembodiment as a cross-coupled p-channel MOSFETs circuit. The enablecircuit 280 is connected to the local bit lines (BL, BLB) and the outputcircuit 220 and is configured to provide the output voltage generated bythe output circuit 220 to the local bit line (BL/BLB).

The voltage generating circuit 290 is connected to the global bit lines(WGBL, WGBLB) and the enable circuit 280 and is configured to provide onthe global bit line (WGBL/WGBLB) a low power consumption voltage, alevel of which, e.g., 900 mV, is lower than the high voltage level,e.g., 1 V, but higher than the low voltage level, e.g., 0 V.

Referring now to FIG. 5, the pass gate circuit 260 includes an enablenode (WPG) and p-channel MOSFETs (M1, M2). The first source/drainterminals of the p-channel MOSFETs (M1, M2) of the pass gate circuit 260are respectively connected to the data lines (DL, DLB). The secondsource/drain terminals of the p-channel MOSFETs (M1, M2) of the passgate circuit 260 are respectively connected to the global bit lines(WGBL, WGBLB). The gate terminals of the p-channel MOSFETs (M1, M2) ofthe pass gate circuit 260 are connected to each other and to the enablenode (WPG).

The keeper 270 includes p-channel MOSFETs (M1, M2). The firstsource/drain terminals of the p-channel MOSFETs (M1, M2) of the keeper270 are connected to each other and to the source voltage node 310. Thesecond source/drain terminal of the p-channel MOSFET (M1) and the gateterminal of the p-channel MOSFET (M2) of the keeper 270 are connected toeach other and to the local bit line (BL). The second source/drainterminal of the p-channel MOSFET (M2) and the gate terminal of thep-channel MOSFET (M1) of the keeper 270 are connected to each other andto the local bit line (BLB).

The enable circuit 280 includes an enable node (WE) and n-channelMOSFETs (M1, M2). The first source/drain terminals of the n-channelMOSFETs (M1, M2) of the enable circuit 280 are respectively connected tothe local bit lines (BL, BLB). The second source/drain terminals of then-channel MOSFETs (M1, M2) of the enable circuit 280 are respectivelyconnected to the first source/drain terminals of the n-channel MOSFETs(M1, M2) of the output circuit 220. The gate terminals of the n-channelMOSFETs (M1, M2) of the enable circuit 280 are connected to each otherand to the enable node (WE).

The memory device 200 further includes a pre-charger 520 connected tothe local bit lines (BL, BLB) and configured to pre-charge the local bitlines (BL, BLB) to the high voltage level. In this exemplary embodiment,the pre-charger 520 includes an enable node (BLPGB) and p-channelMOSFETs (M1, M2). The first source/drain terminals of the p-channelMOSFETs (M1, M2) of the pre-charger 520 are connected to each other andto the source voltage node 310. The second source/drain terminals of thep-channel MOSFETs (M1, M2) of the pre-charger 520 are respectivelyconnected to the local bit lines (BL, BLB). The gate terminals of thep-channel MOSFETs (M1, M2) of the pre-charger 520 are connected to eachother and to the enable node (BLPGB).

Schematic diagrams of the write circuit unit during a write operation ofthe memory device 200, according to some embodiments, are illustrated inFIGS. 7A and 7B. Prior to a write operation, when voltages at the enablenodes (BLPGB, SAPGB) transition from the high voltage level to the lowvoltage level, the p-channel MOSFETs (M1, M2) of the pre-chargers 510,520 are turned on. As a result, the local bit lines (BL, BLB) and thedata lines (DL, DLB) are pre-charged to the high voltage level.Subsequently, when the voltages at the enable nodes (BLPGB, SAPGB)transition from the low voltage level back to the high voltage level,the p-channel MOSFETs (M1, M2) of the pre-chargers 510, 520 are turnedoff. As a result, the local bit lines (BL, BLB) and the data lines (DL,DLB) are left floating at the high voltage level. The global bit lines(WGBL, WGBLB) are also pre-charged to the high voltage level prior to awrite operation as will be described below in conjunction with FIG. 8.

As illustrated in FIG. 7A, during a write operation of the memory device200, in which the voltage generating circuit 290 provides on the globalbit line (WGBL) a low power consumption voltage (VDD-ΔV), a level ofwhich, e.g., 900 mV, is lower than the high voltage level, e.g., 1 V,but higher than the low voltage level, e.g., 0 V, when a voltage at theenable node (WPG) transitions from the high voltage level to the lowvoltage level, the p-channel MOSFETs (M1, M2) of the pass gate circuit260 are turned on and connect respectively and electrically the datalines (DL, DLB) to the global bit lines (WGBL, WGBLB). This transfersthe low power consumption voltage level from the global bit line (WGBL)to the data line (DL). This, in turn, pulls the data line (DL) towardsthe low power consumption voltage level. As this occurs, the data line(DLB) stays at the high voltage level. The p-channel and n-channelMOSFETs (M1, M4) of the sense amplifier 240 are turned off and aretherefore crossed out in FIG. 7A. The pass gate circuit 230 and theenable circuit 250 of the read circuit unit are not in operation and theMOSFETs (M1, M2) thereof are also crossed out in FIG. 7A.

When the sense amplifier 240 senses that a difference between the levelsof the voltages on the data lines (DL, DLB) is greater than a threshold,e.g., 100 mV, a voltage at the enable node (SAE) transitions from thelow voltage level to the high voltage level. This pulls the data line(DL) to the low voltage level. At this time, the enable node (WE) is atthe high voltage level. As a result, the low voltage level istransferred from the data line (DL) to the local bit line (BL) by theoutput circuit 220 through the n-channel MOSFET (M1) of the enablecircuit 280. This pulls the local bit line (BL) to the low voltagelevel. This, in turn, keeps the local bit line (BLB) at the high voltagelevel. The p-channel MOSFET (M1) of the keeper 270 is turned off and istherefore crossed out in FIG. 7A. At this time, the word line (WL) isactivated, whereby complementary bits of data are written to the memorycell 210.

As illustrated in FIG. 7B, during another write operation of the memorydevice 200, in which the voltage generating circuit 290 provides the lowpower consumption voltage (VDD-ΔV) on the global bit line (WGBLB), whena voltage at the enable node (WPG) transitions from the high voltagelevel to the low voltage level, the p-channel MOSFETs (M1, M2) of thepass gate circuit 260 are turned on and connect respectively andelectrically the data lines (DL, DLB) to the global bit lines (WGBL,WGBLB). This transfers the low power consumption voltage level from theglobal bit line (WGBLB) to the data line (DLB). This, in turn, pulls thedata line (DLB) towards the low power consumption voltage level. As thisoccurs, the voltage on the data line (DL) stays at the high voltagelevel. The p-channel and n-channel MOSFETs (M2, M3) of the senseamplifier 240 are turned off and are therefore crossed out in FIG. 7B.The pass gate circuit 230 and the enable circuit 250 of the read circuitunit are not in operation and the MOSFETs (M1, M2) thereof are alsocrossed out in FIG. 7B.

When the sense amplifier 240 senses that a difference between the levelsof the voltages on the data lines (DL, DLB) is greater than a threshold,e.g., 100 mV, a voltage at the enable node (SAE) transitions from thelow voltage level to the high voltage level. This pulls the data line(DLB) to the low voltage level. At this time, the enable node (WE) is atthe high voltage level. As a result, the low voltage level istransferred from the data line (DLB) to the local bit line (BLB) by theoutput circuit 220 through the n-channel MOSFET (M2) of the enablecircuit 280. This pulls the local bit line (BLB) to the low voltagelevel. This, in turn, keeps the local bit line (BL) at the high voltagelevel. The p-channel MOSFET (M2) of the keeper 270 is turned off and istherefore crossed out in FIG. 7B. At this time, the word line (WL) isactivated, whereby complementary bits of data are written to the memorycell 210.

A schematic diagram of an exemplary voltage generating circuit 290 ofthe write circuit unit of the memory device 200, according to someembodiments, is illustrated in FIG. 8. As illustrated in FIG. 8, thevoltage generating circuit 290 is connected to the global bit lines(WGBL, WGBLB) and the enable node (WE) and includes input nodes (DIN,DINB), capacitors (C1), an inverter (INV), and p-channel and n-channelMOSFETs (M1, M2, M3, M4, M5, M6).

In operation, when it is desired to write a bit ‘0’ to the memory cellnode 330, i.e., a bit ‘1’ to the memory cell node 340, low and highvoltage levels are respectively applied to the input nodes (DIN, DINB).This turns the p-channel MOSFETs (M1, M2) on and the p-channel MOSFETs(M3, M4) off. Subsequently, when a voltage at the enable node (WE)transitions from the low voltage level to the high voltage level, then-channel MOSFETs (M5, M6) are turned off. As a result, a low powerconsumption voltage (VDD-ΔV), a level of which, e.g., 900 mV, is lowerthan the high voltage level, e.g., 1 V, but higher than the low voltagelevel, e.g., 0 V, is provided on the global bit line (WGBL). At thistime, the ΔV is calculated using the equation,VDD/(1+(C_(GBL)/(N*C1)))where C_(GBL) is the parasitic capacitance of the global bit line(WGBL), C1 is the capacitance of the capacitor C1, and N is the numberof the capacitors C1.

Conversely, when it is desired to write a bit ‘0’ to the memory cellnode 340, i.e., a bit “1” to the memory cell node 330, low and highvoltage levels are respectively applied to the input nodes (DINB, DIN).This turns the p-channel MOSFETs (M3, M4) on and the p-channel MOSFETs(M1, M2) off. Subsequently, when the voltage at the enable node (WE)transitions from the low voltage level to the high voltage level, then-channel MOSFETs (M5, M6) are turned off. As a result, a low powerconsumption voltage (VDD-ΔV), a level of which, e.g., 900 mV, is lowerthan the high voltage level, e.g., 1 V, but higher than the low voltagelevel, e.g., 0 V, is provided on the global bit line (WGBLB). At thistime, the ΔV is calculated using the equation,VDD/(1+(C_(GBLB)/(N*C1)))where C_(GBLB) is the parasitic capacitance of the global bit line(WGBLB).

In this exemplary embodiment, the voltage generating circuit 290 furtherincludes a pre-charger 810 connected to the source voltage node 310, theglobal bit lines (WGBL, WGBLB), the enable node (WE), and the inverter(INV). In operation, when the enable node (WE) is at the low voltagelevel, i.e., prior to write operations of the memory device 200, thepre-charger 810 connects the global bit lines (WGBL, WGBLB) to thesource voltage node 310. As a result, the pre-charger 810 pre-chargesthe global bit lines (WGBL, WGBLB) to the high voltage level.Thereafter, when the voltage at the enable node (WE) transitions to thehigh voltage level, the global bit lines (WGBL, WGBLB) are left floatingat the high voltage level.

It should be understood that other configurations for the voltagegenerating circuit 290 may be used to generate the low power consumptionvoltage (VDD-ΔV). A schematic diagram of another exemplary voltagegenerating circuit 290 of the write circuit unit of the memory device200, according to some embodiments, is illustrated in FIG. 9. Asillustrated in FIG. 9, the voltage generating circuit 290 includes inputnodes (D, DB), and a pair of circuit modules 910, 920, each of which isconnected to a respective one of the input nodes (D, DB), a respectiveone of the global bit lines (WGBLB, WGBL), and the enable node (WE). Inthis exemplary embodiment, each of the circuit modules 910, 920 includesa NAND gate (NAND), an inverter (INV), and p-channel MOSFETs (M1, M2,M3, M4).

In operation, when it is desired to write a bit ‘0’ to the memory cellnode 330, i.e., a bit ‘1’ to the memory cell node 340, low and highvoltage levels are respectively applied to the input nodes (D, DB).Subsequently, when a voltage at the enable node (WE) transitions fromthe low voltage level to the high voltage level, the p-channel MOSFETs(M1, M2) of the circuit module 920 are turned off and on, respectively.At this time, at least one of the p-channel MOSFETs (M3, M4) of thecircuit module 920 is turned on. As a result, a low power consumptionvoltage (VDD-ΔV), a level of which, e.g., 900 mV, is lower than the highvoltage level, e.g., 1 V, but higher than the low voltage level, e.g., 0V, is provided on the global bit line (WGBL).

Conversely, when it is desired to write a bit ‘1’ to the memory cellnode 330, i.e., a bit “0” to the memory cell node 340, low and highvoltage levels are respectively applied to the input nodes (DB, D).Subsequently, when a voltage at the enable node (WE) transitions fromthe low voltage level to the high voltage level, the p-channel MOSFETs(M1, M2) of the circuit module 910 are turned off and on, respectively.At this time, at least one of the p-channel MOSFETs (M3, M4) of thecircuit module 910 is turned on. As a result, a low power consumptionvoltage (VDD-ΔV), a level of which, e.g., 900 mV, is lower than the highvoltage level, e.g., 1 V, but higher than the low voltage level, e.g., 0V, is provided on the global bit line (WGBLB).

From the above description, the memory device 200 of the presentdisclosure comprises a write circuit unit including a pass gate circuit260 configured to connect electrically and respectively data lines (DL,DLB) to global bit lines (WGBL, WGBLB), and a read circuit unitincluding a pass gate circuit 230 configured to connect electrically andrespectively local bit lines (BL, BLB) to data lines (DL, DLB) and asense amplifier 240 connected to the pass gate circuits 230, 260. Theconstruction as such permits usage of the sense amplifier 240 of theread circuit unit by the write circuit unit during write operations ofthe memory device 200, whereby a low power consumption voltage (VDD-ΔV)can be applied to the global bit line (WGBL/WGBLB) during the writeoperations, thereby reducing power consumption of the memory device 200,e.g., by up to 56%.

In an exemplary embodiment, a memory device comprises a memory cell, alocal bit line coupled to the memory cell, a data line, a first passgate circuit coupled to the local bit line and the data line andconfigured to couple the local bit line to the data line, a global bitline, a second pass gate circuit coupled to the data line and the globalbit line and configured to couple the data line to the global bit line,and a sense amplifier coupled to the data line.

In another exemplary embodiment, a memory device comprises a memorycell, a local bit line coupled to the memory cell, a data line, a passgate circuit coupled to the local bit line and the data line andconfigured to couple the local bit line to the data line, an outputcircuit coupled to the data line and configured to generate an outputvoltage level that corresponds to a voltage level on the data line, andan enable circuit coupled to the local bit line and the output circuitand configured to provide the output voltage level to the local bitline.

In another exemplary embodiment, a memory device comprises a memory cellconfigured to store low and high voltage levels therein, a local bitline coupled to the memory cell, a data line, a first pass gate circuitcoupled to the local bit line and the data line and configured to couplethe local bit line to the data line, a global bit line, a second passgate circuit coupled to the data line and the global bit line andconfigured to couple the data line to the global bit line, and a voltagegenerating circuit coupled to the global bit line and configured toprovide on the global bit line a low power consumption voltage levellower than the high voltage level but higher than the low voltage level.

The foregoing outlines features of several embodiments so that thoseskilled in the art may better understand the aspects of the presentdisclosure. Those skilled in the art should appreciate that they mayreadily use the present disclosure as a basis for designing or modifyingother processes and structures for carrying out the same purposes and/orachieving the same advantages of the embodiments introduced herein.Those skilled in the art should also realize that such equivalentconstructions do not depart from the spirit and scope of the presentdisclosure, and that they may make various changes, substitutions, andalterations herein without departing from the spirit and scope of thepresent disclosure.

What is claimed is:
 1. A memory device comprising: a memory cellconfigured to store low and high voltage levels therein; a local bitline coupled to the memory cell; a data line; a first pass gate circuitcoupled to the local bit line and the data line and configured to couplethe local bit line to the data line; a global bit line; a second passgate circuit coupled to the data line and the global bit line andconfigured to couple the data line to the global bit line; and a voltagegenerating circuit coupled to the global bit line and configured toprovide on the global bit line a low power consumption voltage levellower than a high voltage level but higher than a low voltage level, thelow power consumption voltage level being used during a write operationto identify data to be written to the memory cell.
 2. The memory deviceof claim 1, further comprising a sense amplifier coupled to the dataline.
 3. The memory device of claim 1, further comprising an outputcircuit coupled to the data line and configured to generate an outputvoltage level that corresponds to a voltage level on the data line. 4.The memory device of claim 3, further comprising an enable circuitcoupled to the local bit line and the output circuit and configured toprovide the output voltage level to the local bit line.
 5. The memorydevice of claim 4, wherein the enable circuit is further coupled to thevoltage generating circuit.
 6. The memory device of claim 4, furthercomprising a pre-charger coupled to the global bit line and the enablecircuit and configured to pre-charge the global bit line to the highvoltage level.
 7. The memory device of claim 3, further comprising: asecond global bit line; and an enable circuit coupled to the outputcircuit and the second global bit line and configured to provide theoutput voltage level to the second global bit line.
 8. The memory deviceof claim 1, further comprising a pre-charger coupled to the local bitline and configured to pre-charge the local bit line to the high voltagelevel.
 9. The memory device of claim 1, further comprising a pre-chargercoupled to the data line and configured to pre-charge the data line tothe high voltage level.
 10. A memory device comprising: a memory cellconfigured to store complementary bits of data; a pair of local bitlines coupled to the memory cell; a pair of data lines; a first passgate circuit coupled to a local bit line of the pair of local bit linesand a data line of the pair of data lines and configured to couple tothe local bit line to the data line; a pair of global bit lines; asecond pass gate circuit coupled to the data line and a global bit lineof the pair of global bit lines and configured to couple the data lineto the global bit line; and a voltage generating circuit coupled to thepair of global bit lines and configured to provide on the pair of globalbit lines a low power consumption voltage level lower than a highvoltage level but higher than a low voltage level, the low powerconsumption voltage level being used during a write operation toidentify data to be written to the memory cell.
 11. The memory device ofclaim 10, further comprising a sense amplifier coupled to the pair ofdata lines.
 12. The memory device of claim 10, further comprising anoutput circuit coupled to the data line and configured to generate anoutput voltage level that corresponds to a voltage level on the dataline.
 13. The memory device of claim 12, further comprising an enablecircuit coupled to the local bit line and the output circuit andconfigured to provide the output voltage level to the local bit line.14. The memory device of claim 13, wherein the enable circuit is furthercoupled to the voltage generating circuit.
 15. The memory device ofclaim 13, further comprising a pre-charger coupled to the pair of globalbit lines and the enable circuit and configured to pre-charge the pairof global bit lines to the high voltage level.
 16. The memory device ofclaim 12, further comprising: another enable circuit coupled to theoutput circuit and another global bit line of the pair of global bitlines and configured to provide the output voltage level to the anotherglobal bit line.
 17. The memory device of claim 10, further comprising apre-charger coupled to the pair of local bit lines and configured topre-charge the local bit line to the high voltage level.
 18. The memorydevice of claim 10, further comprising a pre-charger coupled to the pairof data lines and configured to pre-charge the pair of data lines to thehigh voltage level.
 19. A memory device comprising: a memory cell; alocal bit line coupled to the memory cell; a data line; a first passgate circuit coupled to the local bit line and the data line andconfigured to couple the local bit line to the data line; a global bitline; a second pass gate circuit coupled to the data line and the globalbit line and configured to couple the data line to the global bit line;a voltage generating circuit coupled to the global bit line andconfigured to provide on the global bit line a low power consumptionvoltage level lower than a high voltage level but higher than a lowvoltage level, the low power consumption voltage level being used duringa write operation to identify data to be written to the memory cell; anda keeper circuit coupled to the local bit line.
 20. The memory device ofclaim 19, wherein the keeper circuit comprises at least two transistorscoupled to each other.